I usually do things like this by mixing icing sugar with equal amount of cocoa powder, then stir in water (tiny amounts) until it's just gloopy enough to work with. It will set hard, taste chocolatey and although it's sugary, it's only a small amount in total and there's no fat.

You can pipe it out of a plastic food bag with tiny corner snipped off, or make a greaseproof paper cone and snip the tip off. Practise on a plate first.

thank you, would you melt the chocolate in a pan, and add the milk to it? Ive heard that chocolate shouldnt be melted directly, it should be done over a pan of boiling water? if so when would you add milk?